1. Field of the Invention
The present invention relates generally to modulation, and more specifically to rate adjustable differential phase shift key (DPSK) modulation.
2. Background
Optical broadband communication systems generally transmit optical signals through the atmosphere via free space optical communication (FSOC) links and/or through fiber via fiber-optic communication (FOC) links. While such links have many beneficial characteristics, they are also susceptible to a variety of factors that may negatively affect their performance.
For example, most fixed and mobile FSOC links are susceptible to atmospheric variability. Changes in weather conditions (e.g., fog, dust, rain, clouds, etc.) or even free space path loss in a mobile environment can have a significant impact on available link margin. Other less predictable atmospheric conditions, such as turbulence or scintillation, can also substantially affect system performance.
Many techniques have been employed to mitigate channel effects associated with FSOC and FOC links. One such technique involves trading link margin for throughput. This technique has been demonstrated using binary pulse-position modulation (BPPM). However, BPPM does not provide adequate sensitivity. Fixed-rate DPSK has been used to achieve near-quantum limited performance, but attempts to achieve rate adaptability have proven cumbersome and involve the use of many integrated waveguides.
There is a need for rate adjustable DPSK systems and methods that addresses one or more of the aforementioned shortcomings of conventional optical broadband communication systems and methods.
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